Predictions of total water levels, the elevation of combined tides, surge, and wave runup at the shoreline, are necessary to provide guidance on potential coastal erosion and flooding. Despite the importance of early warning systems for these hazards, existing real-time meteorological and oceanographic forecast systems at regional and national scales, until now, have lacked estimates of runup necessary to predict wave-driven overwash and erosion. To address this need, we present an approach that includes wave runup in an operational, national-scale modeling system. Using this system, we quantify the contribution of waves to potential dune erosion events along 4,700?km of U.S. Atlantic and Gulf of Mexico sandy coastlines for a one-year period. Dune erosion events were predicted to occur at over 80% of coastal locations, where waves dominated shoreline total water levels, representing 73% of the signal. This shows that models that neglect the wave component underestimate the hazard. This new, national-scale operational modeling system provides communities with timely, local-scale (0.5?km resolution) coastal hazard warnings for all wave conditions, allowing for rapid decision-making related to safety and emergency management. The modeling system also enables continued research into wave-driven processes at a broad range of coastal areas.

Shoreline change resulting from the landfall of Hurricane Bonnie in 1998 and Hurricane Floyd in 1999 was found to be highly variable along a 100-km stretch of coast in southern North Carolina. Change calculated over a longer, three-year period also showed a large amount of longshore variability: some sections experienced over 50 m of erosion while other areas were nearly stable. Initial analyses focused on two islands where the mean response and longshore variability were strikingly different. Masonboro Island showed a larger magnitude response to Hurricane Floyd and over the cumulative three-year period than the relatively stable Topsail Island. Masonboro experienced over 30 m of shoreline erosion over a three-year period while Topsail Island eroded only 8 m (most of which was attributed to Hurricane Bonnie). The longshore variability of shoreline change was greater on Masonboro Island and increased over the years studied. The standard deviation of shoreline change increased from 6 - 8 m following the hurricanes to 14.5 m over three years. The standard deviation of change on Topsail Island was ~6.7 m for each signal, indicating less longshore variability than on Masonboro Island. Shoreline change on Masonboro was dominated by a trend that revealed more erosion occurring along the southern end of the island. When the trend was removed from the signal, most of the remaining variance was contained at length scales shorter than 500 m. On Topsail, most of the variance of the shoreline change signal was contained at long wavelengths (> 2 km); however, only a small percentage of the variance was contained in a trend.